Channel quality monitoring apparatus

Description

Background of the Invention

[0001] The present invention relates to a quality monitoring apparatus for a communication channel. Specifically, the present invention is concerned with a channel quality monitoring apparatus capable of providing an improved detection accuracy of a channel error rate in a digital radio transmission system.

[0002] In a conventional channel quality monitoring apparatus used in a digital radio transmission system, there has been employed a method of monitoring a frame synchronizing signal or a parity signal etc. generated at a stage of frame synchronization on the basis of a signal received and demodulated in a receiver and demodulator, or a method of generating a preliminary pulse signal including a clock signal or a clock signal added with a predetermined fixed pattern extracted from a signal received and demodulated in a discriminating unit of a demodulator provided in a receiver and demodulator to predict or forecast a channel quality based on the preliminary pulse signal (see Intl. Conference on Communications, Denver, CO-(USA), June 14-18, 1981, vol.2 pages 35.4.1-35.4.3). An error detection based on syndromes according to the preamble of claim 1 is described in IEEE Communications Magazine, vol 21, no.1, January 1983, pages 11 to 19.

[0003] However, drawbacks with such conventional channel quality monitoring apparatus are as follows: First is a limited accuracy in channel quality judgement. Second, a large redundant bit length is required for ensuring a high detection accuracy of channel error rate, resulting in a degraded channel utilization efficiency.

Summary of the Invention

[0004] With the above in view, an object of the present invention is to provide a channel quality monitoring apparatus capable of providing an improved detection accuracy of a channel error rate in an apparatus of receiving and demodulating system.

[0005] A channel quality monitoring system according to the present system is characterized in that a syndrome used for correcting an error code is utilized for monitoring an error rate of a communication channel.

[0006] To realize the above feature, the channel quality monitoring system according to the present invention is configured to combine a syndrome generator operative to generate a predetermined syndrome with a conventional channel monitoring apparatus in order to select an optimum error rate depending upon error occurrence time detected on the basis of the syndrome generated on the receiving side receiving a sent message, and to provide means for detecting an error rate on a communication channel in a predetermined apparatus of receiving and demodulating system provided in terminal equipment of digital radio transmission system, or in a predetermined apparatus of receiving and demodulating system provided in both terminal equipment of digital radio transmission system and a predetermined repeater apparatus.

[0007] Specifically, the channel quality monitoring apparatus provided in terminal equipment of digital radio communication system to monitor an error rate of a receiving signal comprises syndrome generator means responsive to a digital multiplexed signal of the receiving signal to generate a syndrome for correcting code error, converter means for converting the digital multiplexed signal which has undergone error correction based on the syndrome outputted from the syndrome generator means into a second digital multiplexed signal with which a predetermined parity detection is possible, parity detector means for effecting a parity detection of the second digital multiplexed signal outputted from the converter means, and computing means responsive to outputs from the syndrome generator means and the parity detector means, wherein when occurrence of code error detected on the basis of the syndrome generated in the syndrome generator means continues for the duration less than a predetermined time period, the computing means is operative to compute an error rate of the receiving digital multiplexed signal on the basis of the syndrome, while when occurrence of code error detected on the basis of the syndrome continues for the duration equal to or more than the predetermined time period, the computing means is operative to compute an error rate of the receiving digital multiplexed signal on the basis of the output from the parity detector means.

Brief Description of the Drawings

[0008] The feature and advantages of a channel quality monitoring apparatus according to the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a block diagram illustrating an embodiment of a channel quality monitoring apparatus according to the present invention;

Fig. 2 is a block diagram illustrating details of an error rate detector circuit provided in the channel quality monitoring apparatus shown in Fig. 1; and

Fig. 3 is a graph showing a corrected error rate (channel error rate) P versus a syndrome error rate P_s and a parity error rate Pp employed in the present invention.

Description of the Preferred Embodiment

Principle of the Invention

[0009] In accordance with an error correcting scheme using syndrome, in case where an code error of a receiving digital multiplexed signal is fixed, the syndrome of this signal is expressed as "0" indicating that there is no error. The channel quality monitoring system according to the present invention is provided with computing means for eliminating such an undesired phenomenon wherein when occurrence of code error detected on the basis of the syndrome continues for the duration equal to or more than a predetermined time, computing means functioning as an error rate detector executes a processing for computing an error rate of a receiving signal on the basis of a code error detected by parity detector means.

[0010] The definition of the syndrome used in the present invention will be described. It is now assumed that a transmission code vector expressed as a column vector having n components in total comprising K code bits and r parity check bits is represented by a vector T, and that the parity check condition which satisfies the vector Tis symbolically expressed by the relationship

where ÍÌ denotes a parity check matrix with n columns and r rows having the binary symbols of 0 and 1 as their components. It is further assumed that a code received at a receiving terminal of a transmission path is represented by R vector expressed as a column vector having n components, and that the R vector is replaced by the expression

where E is a transmission error vector.

[0011] Further, let us suppose a vector S expressed as follows:

[0012] Thus, it is understood that transmission error can be detected depending upon whether the vector S represents 0 or not. This vector S is called a "syndrome".

Preferred Embodiment

[0013] A preferred embodiment of a channel quality monitoring apparatus according to the present invention will be described with reference to attached drawings.

[0014] As shown in Fig. 1, the channel quality monitoring apparatus in this embodiment comprises an input terminal 1 for a receiving signal 101, a signal branch circuit 10 for branching the signal 101 into signals 102 and 103, a register 11 for holding the signal 102 from the branch circuit 10, a syndrome extracting circuit 12 for extracting a syndrome from the signal 103, an error correcting circuit 13 responsive to an output 108 from the register 11 and an output 107 from the syndrome extracting circuit 12 to effect an error correction, a signal converter circuit 14 for converting a signal 109 subject to an error correction into a signal 112 with which parity detection is possible, a parity detector circuit 15 responsive to the signal 112 from the signal converter circuit 14, and an error rate detector circuit 16 responsive to outputs 104 and 105 from the syndrome extracting circuit 12 and to outputs 110 and 111 from the parity detector circuit 15. In addition, the error rate detector circuit 16 is provided with an error rate output terminal 2.

[0015] Referring to Fig. 2, there are shown details of the error rate detector circuit 16 comprising first error rate computing circuit 161 responsive to the outputs 104 and 105 from the syndrome extractor 12 to produce a first error rate signal based on the syndrome, a second error rate computing circuit 162 responsive to the outputs 110 and 111 from the parity detector 15 to produce a second error rate based on the parity, a comparator 163 for comparing the first error rate based on the syndrome from the first error rate computing circuit 161 with a predetermined error rate to produce an output signal indicative of the compared result, and an error rate selector circuit 164 operative to select either the first error rate based on the syndrome from the first error rate computing circuit 161 or the second error rate based on the parity from the second error rate computing circuit 162 depending upon the output signal indicative of the compared result from the comparator 163.

[0016] The operation of the channel quality monitoring aparatus thus configured will be described.

[0017] The signal 101 including a digital multiplexed signal and a clock signal is inputted to the input terminal 1. The signal 101 thus inputted is branched into signals 102 and 103 in the signal branch circuit 10. The signal 103 is sent to the syndrome extracting circuit 12 to extract a predetermined syndrome. In the syndrome extracting circuit 12, a processing is executed to detect whether an error of the digital multiplexed sigal included in the signal 103 is present or not. Where there occurs an error, a processing is executed to identify an error position. When a check matrix is expressed by H, a syndrome is symbolically expressed by

where Õ denotes a linear code. The syndrome extracting circuit 12 effects an error judgement operation as follows: When

it is judged that there is an error, while when

it is judged that there is no error. As previously described, however, there is a possibility that the syndrome extracting circuit 12 judges the case where error occurrence is fixed as a no-error although an error is actually occurring.

[0018] An example of an error detection using the syndrome will be now referred to. First, on the side of transmitting a message, a technique is employed to divide a transmission data train into a plurality of sub-blocks having a predetermined bit length (e.g. 81 bits) to add a predetermined redundant bit train of 3 bits to each sub-block. Then, a processing based on an error correcting code rule is applied to the three columns of sub-blocks of 81 bits to assign information indicative of error correcting code to the three columns of the redundant bit train of 3 bits, i.e. 9 bits, thus transmitting each data train divided into sub-blocks of 84 bits including the redundant bit train to which the information indicative of error correcting code is assigned.

[0019] On the side of receiving the sent message, a processing based on the same coding rule is applied to the three columns of the divided code trains to provide a syndrome of 9 bits. Thus, an error of the code train (the signal 108 in Fig. 1) can be corrected depending upon the value of the syndrome (the output 107 in Fig. 1) in the error correcting circuit 13. When the value of the syndrome represents zero, it is judged that there is no code error.

[0020] The basic operation of the syndrome extracting circuit 12 is described in detail in the related material (Second forum on information theory and its application, Nov., 1979).

[0021] Thus, the signal 109 including error-corrected digital multiplexed signal and clock signal is obtained as an output of the error correcting circuit 13. In the signal converter circuit 14, this signal 109 is then subjected to a speed conversion for removing redundancy bits which are added to the data with parity bits at the transmission side converted into the signal 112 including digital multiplexed signal and the clock signal, with which a predetermined parity can be detected. The signal 112 thus obtained is inputted to the parity detector circuit 15 to detect an error on the basis of parity check. The syndrome pulse 104 and the clock signal 105 among signals outputted from the syndrome extractor circuit 12 and the parity pulse 110 and the clock signal 111 among signals outputted from the parity detector circuit 15 are inputted to the error rate detector circuit 16 to detect an error rate corresponding to a predetermined time length to output the error rate signal 106 thus detected from the error rate output terminal 2.

[0022] The detailed operation of the error rate detector circuit 16 which is the subject of the present invention will be described.

[0023] Assuming that the number of parity check bits is 1000 and the number of data bits within a syndrome monitoring section is 81, an error rate P which has undergone error correction, an error rate P_s based on the syndrome and an error rate Pp based on the parity are derived as follows:

The relationship between an error rate P' before error correction is made and the above-mentioned corrected error rate P is expressed by the following equation.

[0024] P = K (P')² where K is a constant determined by the data bit n and the error correction system. In the case of a single Lee error correction, K is 125 for n = 81 and P = 125 (P')² stands. In this case,

and

Pp = 1000 P.

[0025] Referring to Fig. 3, there is shown the corrected error rate P versus the error rate P_s based on the syndrome and the error rate Pp based on the parity.

[0026] In general, where a comparison of the parity pulse with the syndrome pulse is continued for a predetermined time period, it is possible to compute an error rate of a communication channel using the number of parity pulses and the number of syndrome pulses. In such a case, it can be said that, within a predetermined time period, the larger the number of pulses to be outputted is, the higher the accuracy is when an error rate is computed.

[0027] In view of this, a cross point X (Fig. 3) of a curve indicative of the error rate P_s based on the syndrome and a curve indicative of the error rate Pp based on the parity is selected as a threshold for presenting channel quality criteria wherein the cross point X in this example is approximately 5 x 10-⁵. When the error rate of the channel is high, an error rate based on the parity is used, while when the error rate thereof is low, an error rate based on the syndrome is used.

[0028] The above-mentioned error rate detector circuit 16 is an example suitable for performing such a function.

[0029] With this circuit, when the first error rate from the first error rate computing circuit 161 is smaller than the predetermined error rate, the comparator 163 produce an output for allowing the selector circuit 164 to select the first error rate signal. In contrast, when the first error rate from the first error rate computing circuit 161 is equal to or greater than the predetermined error rate, the comparator 163 produce an output for allowing the selector circuit 164 to select the second error rate signal. Thus, the selector circuit 164 is operative to output first or second error rate signal selected in accordance with an occurrence time of an error of the receiving digital multiplexed signal, thus realizing an improved detection accuracy of channel error rate.

[0030] In accordance with the channel error detecting method using the syndrome and the parity employed in the channel quality monitoring system in the above-mentioned embodiment, an extremely high detection accuracy can be realized using a less number of redundant bits as compared to the conventional methods.

[0031] The present invention is applicable to digital radio transmission systems based on any modulation schemes.

[0032] As described above, the channel quality monitoring system according to the present invention is configured to effect an extraction of a predetermined syndrome and a parity detection, thereby detecting a channel error, thus advantageously providing a remakably improved detection accuracy of channel error rate.

Claims

1. A channel quality monitoring apparatus provided in terminal equipment of a digital communication system comprising syndrome generator means (12) responsive to a digital multiplexed signal and a clock signal of a receiving signal to generate a syndrome for correcting code error, thereby monitoring an error rate of the receiving signal on the basis of the syndrome generated in said syndrome generator means (12),

characterized in that said channel quality monitoring apparatus further comprises:

converter means (14) for converting the digital multiplexed signal (109) which has undergone error correction based on said syndrome output (107) from said syndrome generator means (12) into a second digital multiplexed signal (112) with which a parity detection is possible;

parity detector means (15) for effecting a parity detection of said second digital multiplexed signal (112) outputted from said converter means (14); and

computing means (16) responsive to outputs from said syndrome generator means (12) and said parity detector means (15), wherein when an occurrence of a code error detected on the basis of said syndrome generated in said syndrome generator means (12) continues for the duration less than a predetermined time period, said computing means is operative to compute an error rate of said received digital multiplexed signal on the basis of said syndrome, while when occurrence of code error detected on the basis of said syndrome continues for the duration equal to or more than said predetermined time period, said computing means (16) is operative to compute an error rate of said receiving digital multiplexed signal on the basis of said output from said parity detector means (15).

2. A channel quality monitoring apparatus as set forth in claim 1, which further comprises a signal branch circuit (10) for branching a signal (101) including said digital multiplexed signal and a clock signal into first (102) and second (103) signals.

3. A channel quality monitoring apparatus as set forth in claim 2, which further comprises a register (11) for holding said first signal (102).

4. A channel quality monitoring apparatus as set forth in claim 2 or 3, wherein said syndrome generator means (12) is comprised of a circuit for extracting a syndrome with respect to said digital multiplexed signal included in said second signal (103) to detect as to whether there is an error in said digital multiplexed signal or not.

5. A channel quality monitoring apparatus as set forth in claim 4, which further comprises an error correcting circuit (13) responsive to an output (108) from said register (11) and said output (107) from said syndrome extracting circuit (18) to produce an error-corrected signal (109).

6. A channel quality monitoring apparatus as set forth in claim 4 or 5, wherein said computing means (16) is configured as an error rate detector circuit comprising a first error rate computing circuit (161) responsive to said output from said syndrome generator means (12) to produce a first error rate signal, a second error rate computing circuit (162) responsive to said output from said parity detector circuit (15) to produce a second error rate signal, a comparator (163) for comparing said first error rate signal from said first error rate computing circuit (161) with a predetermined error rate to produce an output signal indicative of the compared result, and an error rate selector circuit (164) adapted to input said first error rate signal from said first error rate computing circuit (161), said output signal indicative of the compared result from said comparator circuit (163), and said second error rate signal from said second error rate computing circuit (162) wherein when said first error rate is smaller than said predetermined error rate, said error rate selector circuit (164) is operative to output said first error rate signal, while when said first error rate is equal to or greater than said predetermined error rate, said selector circuit (164) is operative to output said second error rate signal.

Revendications

1. Appareil de surveillance de la qualité d'une liaison prévu dans un équipement terminal d'un système de transmission numérique comprenant un moyen de générateur de syndrome (12) sensible à un signal multiplexé numérique et à un signal d'horloge d'un signal reçu pour produire un syndrome pour corriger l'erreur de code, surveillant de ce fait un taux d'erreur du signal reçu sur la base du syndrome produit dans le moyen de générateur de syndrome (12),

caractérisé en ce que l'appareil de surveillance de la qualité d'une liaison comprend de plus :

un moyen de convertisseur (14) pour convertir le signal multiplexé numérique (109) qui a subi la correction d'erreur basée sur la sortie du syndrome (107) depuis le moyen de générateur de syndrome (12) en un second signal multiplexé numérique (112) sur lequel la détection de parité est possible ;

un moyen de détecteur de parité (15) pour effectuer une détection de parité du second signal multiplexé numérique (112) sorti depuis le moyen de convertisseur (14), et

un moyen de calcul (16) sensible aux sorties depuis le moyen de générateur de syndrome (12) et depuis le moyen de détecteur de parité (15), dans lequel lorsqu'une présence d'une erreur de code déjectée sur la base du syndrome produit dans le moyen de générateur de syndrome (12) se poursuit pendant une durée inférieure à une période de temps prédéterminée, le moyen de calcul est actif pour calculer un taux d'erreur du signal multiplexé numérique reçu sur la base du syndrome, tandis que lorsque la présence d'une erreur de code détectée sur la base du syndrome se poursuit pendant une durée égale à ou supérieure à la période de temps prédéterminée, le moyen de calcul (16) est actif pour calculer un taux d'erreur du signal multiplexé numérique reçu sur la base de la sortie provenant du moyen de détecteur de parité (15).

2. Appareil de surveillance de la qualité d'une liaison selon la revendication 1, qui comprend de plus un circuit de dérivation de signal (10) pour dériver un signal (101) comportant le signal multiplexé numérique et un signal d'horloge en premier (102) et second (103) signaux.

3. Appareil de surveillance de la qualité d'une liaison selon la revendication 2, qui comprend de plus un registre (11) pour mémoriser le premier signal (102).

4. Appareil de surveillance de la qualité d'une liaison selon la revendication 2 ou 3, dans lequel le moyen de générateur de syndrome (12) est constitué d'un circuit pour extraire un syndrome par rapport au signal multiplexé numérique inclus dans le second signal (103) afin de détecter s'il existe oui ou non une erreur dans le signal multiplexé numérique.

5. Appareil de surveillance de la qualité d'une liaison selon la revendication 4, qui comprend de plus un circuit de correction d'erreur (13) sensible à une sortie (108) depuis le registre (11) et à une sortie (107) depuis le circuit d'extraction de syndrome (12) pour produire un signal d'erreur corrigée (109).

6. Appareil de surveillance de la qualité d'une liaison selon la revendication 4 ou 5, dans lequel le moyen de calcul (16) est configuré comme un circuit détecteur de taux d'erreur comprenant, un premier circuit de calcul de taux d'erreur (161) sensible à la sortie depuis le moyen de générateur de syndrome (12) pour produire un premier signal de taux d'erreur, un second circuit de calcul de taux d'erreur (162) sensible à la sortie depuis le circuit détecteur de parité (15) pour produire un second signal de taux d'erreur, un comparateur (163) pour comparer le premier signal de taux d'erreur provenant du premier circuit de calcul de taux d'erreur (161) à un taux d'erreur prédéterminé pour produire un signal de sortie indicatif du résultat comparé, et un circuit de sélection de taux d'erreur (164) prévu pour entrer le premier signal de taux d'erreur depuis le premier circuit de calcul de taux d'erreur (161), le signal de sortie indicatif du résultat comparé depuis le circuit de comparateur (163), et le second signal de taux d'erreur depuis le second circuit de calcul de taux d'erreur (162) dans lequel lorsque le premier taux d'erreur est inférieur au taux d'erreur prédéterminé, le circuit de sélection de taux d'erreur (164) est actif pour sortir le premier signal de taux d'erreur, tandis que lorsque le premier taux d'erreur est égal à ou supérieur au taux d'erreur prédéterminé, le circuit de sélection (164) est actif pour sortir le second signal de taux d'erreur.

Ansprüche

1. Gerät zur Überwachung der Kanalqualität, das in der Anschlußeinrichtung eines digitalen Übertragungssystems vorgesehen ist, mit einer Anzeichengeneratoreinrichtung (12), die auf ein digitales multiplextes Signal und ein Taktsignal eines Empfangssignals anspricht, um ein Anzeichen zum Korrigieren eines Codefehlers zu erzeugen und dadurch eine Fehlerrate des Empfangssignals auf der Basis des in der Anzeichengeneratoreinrichtung (12) erzeugten Anzeichens zu überwachen,
dadurch gekennzeichnet, daß das Gerät zur Überwachung der Kanalqualität aufweist:

eine Wandlereinrichtung (14), um das digitale multiplexte Signal (109), das einer Fehlerkorrektur auf der Basis des Anzeichenausgangs (107) der Anzeichengeneratoreinrichtung (12) unterzogen worden ist, in ein zweites digitales multiplextes Signal (112) umzuwandeln, mit dem eine Paritätsfeststellung möglich ist;

eine Paritäts-Detektoreinrichtung (15) zum Feststellen einer Parität des zweiten digitalen multiplexten Signals (112), das von der Wandlereinrichtung (14) ausgegeben wurde; und

eine Recheneinrichtung (16), die auf Ausgänge aus der Anzeichengeneratoreinrichtung (12) und der Paritäts-Detektoreinrichtung (15) anspricht, wobei dann, wenn ein Codefehler, der auf der Basis des in der Anzeichengeneratoreinrichtung (12) erzeugten Anzeichens festgestellt wurde, über eine Zeitdauer, die geringer als eine vorbestimmte Zeitperiode ist, dauernd auftritt, die Recheneinrichtung eine Fehlerrate des empfangenen digitalen multiplexten Signals auf der Basis des Anzeichens berechnet, während dann, wenn der Codefehler, der auf der Basis des Anzeichens festgestellt wurde, über eine Zeitdauer andauert, die gleich oder größer als die vorbestimmte Zeitperiode ist, die Recheneinrichtung (16) eine Fehlerrate des empfangenen digitalen multiplexten Signals auf der Basis des Ausgangs der Paritäts-Detektoreinrichtung (15) berechnet.

2. Gerät zur Überwachung der Kanalqualität ferner mit einem Signalverzweigungsschaltkreis (10), um ein Signal (101), das das digitale multiplexte Signal und ein Taktsignal einschließt, in erste und zweite Signale (102 bzw. 103) zu verzweigen.

3. Gerät zur Überwachung der Kanalqualität nach Anspruch 2, ferner mit einem Register (11) zum Halten des ersten Signals (102).

4. Gerät zur Überwachung der Kanalqualität nach Anspruch 2 oder 3, wobei die Anzeichengeneratoreinrichtung (12) einen Schaltkreis zum Extrahieren eines Anzeichens bezüglich des digitalen multiplexten Signals, das in dem zweiten Signal (103) enthalten ist, aufweist, um festzustellen, ob ein Fehler in dem digitalen multiplexten Signal enthalten ist oder nicht.

5. Gerät zum Überwachen der Kanalqualität nach Anspruch 4, ferner mit einem Fehlerkorrekturschaltkreis (13), der auf einen Ausgang (108) des Registers (11) und den Ausgang (107) des Schaltkreises (12) zum Extrahieren des Anzeichens anspricht, um ein fehler-korrigiertes Signal (109) zu erzeugen.

6. Gerät zum Überwachen der Kanalqualität nach Anspruch 4 oder 5, wobei die Recheneinrichtung (16) als ein Fehlerraten-Detektorschaltkreis ausgebildet ist, der aufweist: einen ersten Fehlerraten-Berechnungsschaltkreis (161), der auf den Ausgang der Anzeichengeneratoreinrichtung (12) anspricht, um ein erstes Fehlerraten-Signal zu erzeugen, einen zweiten Fehlerraten-Berechnungsschaltkreis (162), der auf den Ausgang des Paritäts-Detektorschaltkreises (15) anspricht, um ein zweites Fehlerraten-Signal zu erzeugen, einen Komparator (163) zum Vergleichen des ersten Fehlerraten-Signals aus dem ersten Fehlerraten-Berechnungsschaltkreis (161) mit einer vorbestimmten Fehlerrate, um ein Ausgangssignal zu erzeugen, das das verglichene Ergebnis anzeigt, und einen Fehlerraten-Auswahlschaltkreis (164), um das erste Fehlerraten-Signal aus dem ersten Fehlerraten-Berechnungsschaltkreis (161), das Ausgangssignal, das das verglichene Ergebnis aus dem Komparator (163) anzeigt, und das zweite Fehlerraten-Signal aus dem zweiten Fehlerraten-Berechnungsschaltkreis (162) einzugeben, wobei der Fehlerraten-Auswahlschaltkreis (164) das erste Fehlerraten-Signal dann ausgibt, wenn die erste Fehlerrate kleiner als die vorbestimmte Fehlerrate ist, und der Auswahlschaltkreis (164) das zweite Fehlerraten-Signal dann ausgibt, wenn die erste Fehlerrate gleich oder größer als die vorbestimmte Fehlerrate ist.

Drawing